1. Field of the Invention
The present invention relates to an improved coal liquefaction process. More particularly, the invention relates to a process comprising pretreatment of solid coal particles with a vapor phase hydrogen donor solvent followed by coal liquefaction in the presence of a liquid phase solvent.
2. Description of the Prior Art
Coal liquefaction processes in which coal with or without a diluent is subjected to elevated temperatures and pressures to convert the coal to normally liquid hydrocarbonaceous products are well known. Coal liquefaction processes in which coal is converted in the presence of a hydrogen donor diluent with or without added molecular hydrogen are also known. See, for example, U.S. Pat. No. 3,645,885; U.S. Pat. No. 3,617,513 and U.S. Pat. No. 3,841,991, the teachings of which are hereby incorporated by reference.
It is also known to liquify coal in the presence of a vapor phase solvent or in the presence of a vapor phase solvent which comprises a hydrogen donor, see, for example, U.S. Pat. No. 3,997,424 and U.S. Pat. No. 4,036,731.
U.S. Pat. No. 3,970,541 discloses a process for the extraction of coal. The coal and solvent are heated to 370.degree. C. at a rate of 20.degree. C. per minute and, thereafter, to 400.degree. to 500.degree. C. at a rate of less than 10.degree. C. per minute. The solvent is preferably in the gas phase over the greater part of the range in which the slower rate of heating is performed.
U.S. Pat. No. 3,692,662 discloses a staged coal liquefaction process in which a slurry of coal in a solvent, such as a hydrogen donor solvent, is maintained at a temperature below 700.degree..sup.+ to effect formation of a dispersion and, thereafter, the dispersed slurry is heated to a temperature above 700.degree. F.
U.S. Pat. No. 3,791,957 discloses a coal pretreatment at a pressure in excess of 1000 psig in the presence of added hydrogen at a temperature from 600.degree. to 750.degree. F. followed by catalytic ebullating bed coal hydrogenation.
It is also known to produce liquid hydrocarbons by a fluid coking process in which coal particles are slurried in a hydrogen donor solvent (see U.S. Pat. No. 3,841,991). Fluid coking of coal in a water slurry is also known (see U.S. Pat. No. 3,272,720).
It has now been found that pretreatment of solid coal particles with a vapor phase hydrogen donor solvent gives improved coal liquefaction results, such as an increase yield of coal liquids.